On demand oil dispensing systems have been in use for many years to dispense oil or other non-compressible fluid products. These systems are used to change fluids in vehicles, initial filling of new equipment and the general transfer of fluids. Up until the present time almost all of these systems have employed an air operated pumping system that consists of an air compressor to supply pressurized air, regulators and filters to control air pressure and to condition the air to remove moisture and contaminates from the air, an air operated pump to pump the fluid, plumbing to route the fluid to the desired location and a hose end valve or valve and meter to turn the system on and off or if a meter is used to turn the system on and off and to measure the fluid dispensed. The air pumps have consisted of a reciprocating air operated cylinder with the appropriate valving to produce the automatic reciprocating cylinder motion. The air pump is physically connected to a second cylinder that also reciprocates and is connected to the fluid source that pumps the fluid being dispensed. The second cylinder has the appropriate valving to function as a pump. The pressure that can be obtained on the fluid being dispensed is determined by the air pressure to the air cylinder and the ratio of the areas of the air cylinder and the fluid-pumping cylinder. For example, if the air pressure 100 psi is used and the area ratio of the cylinders is 5 to 1, the maximum fluid pressure would be 500 psi.
This system becomes a demand type system since when the fluid flow is blocked, the air pressure increases to the regulated pressure and the air cylinder stalls. When the pressure is relieved by opening a valve, the fluid pressure drops and the air pump reciprocates pumping fluid. This is a very desirable feature since the operator only opens or closes a valve to dispense fluid and the system produces flow on demand.
This type system also has many disadvantages which are as follows:
A large horsepower air compressor is required.
The air compressor and air pump both produce high noise levels.
The system is very inefficient due to the many conversions of power; electrical power is converted to pressurized air by the air compressor; the compressed air is converted to linear force by the air cylinder; and the linear force is converted to fluid pressure by the fluid cylinder. Each of these power conversions produce efficiency losses to the point that output power is less than 10% of input power.
This system is sensitive to any moisture or contaminants in the air that may cause sticking in the air pump valving or wear in the air cylinder due to moisture and contaminants.
The output fluid flow in this system is inversely proportional to the fluid pressure. At no outlet pressure the system produces maximum flow and at maximum outlet pressure the system produces zero flow.
The output flow and discharge pressure pulsated due to the reciprocating nature of the pump. Each time the cylinder reaches the end of the stroke and reverses directions, the output flow stops and the pressure drops. This causes pulsation in the system that is not desirable.
The installed cost of this type system is high due to the many components required to make a functional system. The need for a large air compressor if the air compressor is not required for other uses is a major cost.
The reliability of this type system is less than desirable due to the contamination sensitivity of the air pump valving, seal wear on the cylinder without lubrication and the many components required in the system.
The present invention eliminates the use of compressed air for the on-demand system. This system consists of an electric motor driven gear pump that is connected to the fluid source. The outlet of the gear pump employs a reverse flow check valve to trap pressure between the reverse flow check valve and the hose end shut-off valve. A pressure-sensing switch senses the pressure trapped in the system and, at a pre-set pressure, signals the electrical circuit to disconnect power to the electric motor to turn the pumping system off. When the hose end shut-off valve is opened, the pressure in the circuit drops below the pressure switch setting and electrical power is supplied to the motor starting the pump. As long as the hose end shut-off valve is open and the pressure is below the pressure switch setting, the pumping system stays on. When the hose end shut-off valve is closed, the pressure rises above the pressure switch setting and the system stops.
Since the electric motor is still rotating when the hose end shut-off valve is closed, a pressure relief valve must be connected to the pump outlet to prevent excessive pressure build up when the pump outlet is blocked. This relief valve serves two functions. First, the relief valve prevents excess pressure build up. Secondly, the relief valve allows a pressure higher than the pressure switch setting to be trapped in the system between the reverse flow check valve and the hose end shut-off valve. This is desirable since the pressure switch would signal the pump to turn on with a very small loss of pressure in the system due to thermal contraction of the fluid or any fluid leakage past the reverse flow check valve or the hose end shut-off valve. Since the electric motor is turning at normal operating speed, when the hose end meter is closed the motor has inertia which will continue to turn the pump after the hose end shut-off valve is closed and the pump will continue to pump fluid until the motor stops. Therefore, the pressure relief valve can be set at a pressure greater than the pressure switch setting to get a trapped pressure higher than the pressure switch setting.
It is also necessary to install a reverse flow check valve in the pump inlet. This check valve prevents fluid from draining from the pump when not running. This check valve assures the pump will prime instantly when started and also eliminates any air in the system that may cause error in the dispensing volume since air in the fluid system could cause error in the hose end meter reading.
Advantages of the present invention include:
Output flow is essentially constant with increased output pressure up to the pressure setting.
The output flow is continuous and non-pulsating.
The noise level of the pumping system is very low compared to the air operated systems.
System cost is much less than an air system due to fewer components and the elimination of an air compressor.
The system is many times more efficient than an air system. A 0.5 horsepower system will generate as much or more output horsepower as a 5 horsepower air driven system.
The system is more reliable since the problem of contaminated air is eliminated.
Installation cost is lower since air lines, air filters, air regulators and lubricators are not required.
The electrical operating costs are much lower due to system efficiency.